JP3752002B2 - Optical fiber amplifier - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber amplifying apparatus that amplifies an input optical signal using an Er ³⁺ ion-doped silica optical fiber in an optical communication system, and more particularly to an optical fiber amplifying apparatus having an expanded amplification band.
[0002]
[Prior art]
In an optical communication system that is currently in practical use, an optical amplifying device is provided for each predetermined distance in order to compensate for attenuation of signal light due to loss in an optical fiber transmission line.
As the optical amplifying device, there is an optical fiber amplifying device using an Er ³⁺ ion-doped silica optical fiber.
The optical fiber amplifier, when propagating the excitation light outputted from the pumping light source for the Er ³⁺ ions for amplification in doped optical fiber, the energy level Er ³⁺ ions is higher by the excitation light Excitation gives an energy inversion distribution. When an optical signal to be amplified propagates in the optical fiber excited by the Er ³⁺ ions, stimulated emission is caused by the optical signal, and the propagating optical signal is amplified.
[0003]
This optical fiber amplifying device is easy to couple with the optical fiber for transmission and has good matching, the amplification characteristic has no polarization dependence, and the electric circuit can be greatly reduced. There are various advantages such as cost reduction.
Incidentally, in recent years, in optical communication systems, with an increase in the density of transmission information, there is a demand for an increase in transmission capacity of transmission lines and an increase in transmission capacity by wavelength multiplexing.
[0004]
In wavelength multiplexing transmission scheme described above, the flatness of the gain for each wavelength of the optical amplifying device, the amplification band becomes a problem.
As a method of expanding the amplification band of an optical fiber amplifying device using an Er ³⁺ ion-doped optical fiber, a method of co-doping Al in addition to Er ³⁺ ions in the optical fiber is used. For example, FIG. 5 shows the amplification characteristics with respect to the wavelength when only Er ³⁺ ions are doped, and FIG. 6 shows the amplification characteristics with respect to the wavelength when Er ³⁺ ions are co-doped with Al.
It can be seen that the amplification band with respect to the wavelength is expanded when Al is co-doped as compared with the case where only Er ³⁺ ions are doped.
[0005]
[Problems to be solved by the invention]
However, even when Al is co-doped, the upper limit of the amplification wavelength is up to about 1.560 μm. Normally, 1.550 μm to 1.560 μm, which has a relatively flat gain characteristic with respect to the wavelength, is used as an amplification band in wavelength division multiplexing transmission. The number of wavelengths that can be arranged in this wavelength band is limited to about 4 to 8 waves due to restrictions such as the wavelength stability of the light source and the wavelength stability of the optical multiplexer / demultiplexer.
Therefore, in order to perform a larger number of wavelength multiplexing, it is necessary to expand the amplification band for the wavelength of the optical fiber amplifier.
In expanding the amplification band, the 1.48 μm band is the wavelength band of the excitation light source, and it is not practically preferable to expand the amplification band to the short wavelength side.
Therefore, in order to expand the amplification band, it is necessary to expand the amplification band to a longer wavelength side from the already used 1.550 μm to 1.560 μm.
[0006]
SUMMARY OF THE INVENTION An object of the present invention is to provide an optical fiber amplifying apparatus that solves the above-described problems and that allows a large number of wavelengths to be multiplexed by expanding the amplification band to the long wavelength side.
[0007]
[Means for Solving the Problems]
The present invention has the following means in order to solve the above problems.
[0008]
Optical fiber amplifier according to claim 1 of the present invention is excited by excitation light of a long wavelength band from 1.50μm to Er ³⁺ ions Er ³⁺ ion-doped silica-based optical fiber, ⁴ I ₁₅ of Er ³⁺ ions _{/ 2} level and the ⁴ I _13/2 level form an inversion distribution, and stimulated emission based on this inversion distribution makes the wavelength longer than 1.50 μm incident on the Er ³⁺ ion-doped silica optical fiber. in the optical fiber amplifier for amplifying an optical signal band, with use of the stimulated emission light generated from the Er ³⁺ ion-doped silica optical fiber for excitation light than the 1.50μm as the excitation light of a long wavelength band, 1.48 mu m band or it is characterized by using in combination the excitation light 0.98 mu m band.
[0009]
The optical fiber amplifying device according to claim 2 of the present invention is characterized in that the Er ³⁺ ion-doped silica optical fiber for excitation light has a resonator structure .
[ 0010 ]
According to the optical fiber amplifier of the present invention, the amplification band is expanded to the long wavelength side as follows.
In Er ³⁺ ion-doped silica optical fiber, the ⁴ I _15/2 level and ⁴ I _13/2 level of Er ³⁺ ions are _decoupled and divided into several sub-levels as shown in FIG. The absorption spectrum is a superposition of transitions between these sub-levels as shown in FIG.
Therefore, a four-level optical amplifying apparatus can be configured by combining an appropriate excitation wavelength and signal wavelength.
[ 0011 ]
Here, in order to expand the amplification band of an optical fiber amplifying device using an Er ³⁺ ion-doped silica optical fiber to a longer wavelength side than 1.560 μm, by selecting an excitation wavelength in the 1.53 μm band, An amplification band is obtained in the 1.58 μm band as shown in FIG. Thereby, it is achieved that the amplification band of the optical fiber amplifying device is expanded to the long wavelength side.
On the other hand, the pump light sources currently in practical use are the 1.48 μm and 0.98 μm bands, and no practical pump light source in the 1.53 μm band has been developed.
Therefore, since the Er ³⁺ ion-doped optical fiber doped only Er ³⁺ ions have an emission spectrum 1.53μm band as shown in FIG. 5, an optical fiber amplifier of the present invention, the 1.53μm band The light emission spectrum is used as an excitation light source and the amplification band is expanded to the long wavelength side.
[ 0012 ]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail by embodiments.
(Embodiment 1)
FIG. 1 shows an embodiment of an optical fiber amplifier according to the present invention.
In FIG. 1, an optical fiber amplifying apparatus 1 includes an Er ³⁺ ion-doped optical fiber 2 for excitation light doped only with Er and an Er ³⁺ ion-doped optical fiber 3 doped with Al in addition to Er. . An Er ³⁺ ion-doped optical fiber 2 for excitation light and an Er ³⁺ ion-doped optical fiber 3 doped with Al in addition to Er are connected via an optical multiplexer / demultiplexer 4.
[ 0013 ]
An excitation light source 5 is connected to the input end of the Er ³⁺ ion-doped optical fiber 2, and an optical isolator 6 is connected to the output end. The output end of the optical isolator 6 is connected to the input end of the optical multiplexer / demultiplexer 4. The optical multiplexer / demultiplexer 4 is connected to an input end 7 of signal light and an input end of an Er ³⁺ ion-doped optical fiber 3. An optical isolator 9 is connected to the output side of the Er ³⁺ ion-doped optical fiber 3 via an optical multiplexer / demultiplexer 8, and a signal light output terminal 10 is connected to the output side of the optical isolator 9. In the figure, reference numeral 11 denotes an excitation light source for the Er ³⁺ ion-doped optical fiber 3, and the excitation light from the excitation light source 11 enters the Er ³⁺ ion-doped optical fiber 3 via the optical multiplexer / demultiplexer 8.
[ 0014 ]
The optical fiber amplifier configured as described above operates as follows.
When pump light of 1.48 μm is used as the pumping light source 5 of the Er ³⁺ ion-doped optical fiber 2 for the pump light in the previous stage, 1.53 μm band stimulated emission light is emitted from the Er ³⁺ ion-doped optical fiber 2.
The 1.53μm band of the induced emission light is guided to the subsequent stage of the Er ³⁺ ion-doped optical fiber 3 to excite the signal light input from the signal light output end 10 at a later stage of the Er ³⁺ ion-doped optical fiber 3. The 1.53 μm band excitation light mainly contributes to amplification in a wavelength region of 1.56 μm or more as shown in FIG.
[ 0015 ]
On the other hand, pump light of 1.48 μm is simultaneously incident on the subsequent Er ³⁺ ion-doped optical fiber 3 from the pump light source 11. The excitation light source 11 mainly contributes to amplification in the 1.55 μm to 1.56 μm band.
In this way, 1.48 μm pumping light is amplified by the preceding Er ³⁺ ion-doped optical fiber 2 to be 1.53 μm band stimulated emission light, and this stimulated emission light is pumped by the subsequent Er ³⁺ ion-doped optical fiber 3. By using it as light, the amplification band is expanded to the long wavelength side, thereby providing a broadband optical amplifier.
[ 0016 ]
(Embodiment 2)
FIG. 2 shows another embodiment of the optical fiber amplifier of the present invention.
In FIG. 2, an optical fiber amplifying apparatus 1A includes an Er ³⁺ ion-doped optical fiber 2 for excitation light doped only with Er and an Er ³⁺ ion-doped optical fiber 3 doped with Al in addition to Er. . It is connected via an optical coupler 4 to the Er ³⁺ ion-doped optical fiber 3 doped with Al in addition to the Er ³⁺ ion-doped optical fiber 2 and Er for excitation light from the first embodiment It is the same.
[ 0017 ]
A feature of the optical fiber amplifying apparatus 1A of the second embodiment is that a reflector 22 is provided on the input end side of the Er ³⁺ ion-doped optical fiber 2 via an optical multiplexer / demultiplexer 21. The excitation light source 5 is also connected to the Er ³⁺ ion-doped optical fiber 2 through the optical multiplexer / demultiplexer 21.
Since other configurations are the same as those in the first embodiment, the same parts are denoted by the same reference numerals, and detailed description thereof is omitted.
By providing the reflector 22 on the input end side of the Er ³⁺ ion-doped optical fiber 2, of the stimulated emission light amplified by the Er ³⁺ ion-doped optical fiber 2, the input side of the Er ³⁺ ion-doped optical fiber 2 By reflecting the stimulated emission light traveling in the direction of 1.53 μm, the 1.53 μm band stimulated emission light can be efficiently coupled to the Er ³⁺ ion-doped optical fiber 3.
[ 0018 ]
(Embodiment 3)
FIG. 3 shows still another embodiment of the optical fiber amplifier of the present invention.
In FIG. 3, an optical fiber amplifying apparatus 1B includes an Er ³⁺ ion-doped optical fiber 2 for excitation light doped only with Er and an Er ³⁺ ion-doped optical fiber 3 doped with Al in addition to Er. . It is connected via an optical coupler 4 to the Er ³⁺ ion-doped optical fiber 3 doped with Al in addition to the Er ³⁺ ion-doped optical fiber 2 and Er for excitation light from the first embodiment It is the same.
[ 0019 ]
A feature of the optical fiber amplifying apparatus 1B of the third embodiment is that reflectors 32A and 32B are provided at both ends of the Er ³⁺ ion-doped optical fiber 2. The pumping light source 5 is connected to the Er ³⁺ ion-doped optical fiber 2 via the optical multiplexer / demultiplexer 21 as in the second embodiment.
Since other configurations are the same as those in the first embodiment, the same parts are denoted by the same reference numerals, and detailed description thereof is omitted.
Reflectors 32A, by providing at both ends of the Er ³⁺ ion-doped optical fiber 2 to 32B, by resonating the induced emission light amplified by the Er ³⁺ ion-doped optical fiber 2, stimulated emission light of 1.53μm band It can be efficiently coupled to the Er ³⁺ ion-doped optical fiber 3.
[ 0020 ]
(Other embodiments)
In the above embodiment, 1.48 μm pumping light is used as the pumping light source 5 of the Er ³⁺ ion-doped optical fiber 2 and the pumping light source 11 of the Er ³⁺ ion-doped optical fiber 3, but the pumping light is reduced to 1.48 μm. not limited, may have use pump light of 0.98 .mu.m, it may also be used excitation light 1.48μm and 0.98 .mu.m simultaneously.
[ 0021 ]
【The invention's effect】
As described above, according to the optical fiber amplifier according to claim 1 of the present invention, the excitation light and stimulated emission light generated by Er ³⁺ ion-doped silica-based optical fiber Er ³⁺ ion-doped silica-based optical fiber by, conventionally possible to expand the amplification bandwidth which can not be obtained on the long wavelength side and Do Ri, also, Er pumping light as the excitation light of the Er ³⁺ ions doped silica-based optical fiber ³⁺ ions doped quartz with use of the stimulated emission light generated from the system optical fiber, that by using in combination the excitation light 1.48 mu m band or 0.98 mu m band, to widen the amplification bandwidth to expand the amplification bandwidth to the long wavelength side It has become possible.
[ 0022 ]
According to the optical fiber amplifier according to claim 2 of the present invention, since the Er ³⁺ ions doped silica optical fiber for excitation light has a resonator structure, Er pumping light ³⁺ doped silica-based optical fiber the stimulated emission light can be coupled efficiently to the Er ³⁺ ion-doped optical fiber.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an embodiment of an optical fiber amplifier according to the present invention.
FIG. 2 is an explanatory view showing another embodiment of the optical fiber amplifier of the present invention.
FIG. 3 is an explanatory diagram showing another embodiment of the optical fiber amplifier of the present invention.
FIG. 4 is an explanatory diagram showing amplification characteristics when an Er ³⁺ ion-doped optical fiber is excited in a 1.53 μm band.
FIG. 5 is an explanatory diagram showing amplification characteristics of an optical fiber doped only with Er ³⁺ ions.
FIG. 6 is an explanatory diagram showing amplification characteristics of an Er ³⁺ ion-doped optical fiber co-doped with Al.
It is a diagram showing a state where divided into sublevels unwinds degeneracy of the ⁴ I _15/2 rank and ⁴ I _13/2 order of Er ³⁺ ions in the 7 Er ³⁺ ion-doped silica-based optical fiber .
FIG. 8 is an explanatory diagram showing absorption characteristics of an optical fiber doped with Er ³⁺ ions.
[Explanation of symbols]
DESCRIPTION OF ^SYMBOLS 1 Optical fiber amplifier 2 Er3 ⁺ ion doped optical fiber 3 for excitation light 3 Er3 ⁺ ion doped optical fiber 4 Optical multiplexer / demultiplexer 5 Excitation light source 6 Optical isolator 7 Signal light input 8 Optical multiplexer / demultiplexer 9 Optical isolator DESCRIPTION OF SYMBOLS 10 Output end of signal light 11 Excitation light source 21 Optical multiplexer / demultiplexer 22 Reflector 32A Reflector 32B Reflector

Claims (2)

The Er ³⁺ ions Er ³⁺ ion-doped silica-based optical fiber is excited by the excitation light of a long wavelength band than 1.50 .mu.m, and ⁴ I _15/2 level and ⁴ I _13/2 level of Er ³⁺ ions In an optical fiber amplifying apparatus for amplifying an optical signal having a wavelength longer than 1.50 μm incident on the Er ³⁺ ion-doped silica-based optical fiber by forming an inversion distribution between the two, and by stimulated emission based on the inversion distribution, with use of the stimulated emission light generated from the Er ³⁺ ion-doped silica optical fiber for excitation light as the excitation light of a long wavelength band than the 1.50 .mu.m, is used in combination with excitation light of 1.48 mu m band or 0.98 mu m band An optical fiber amplifying device. Fiber amplifier equipment according to claim 1, excitation light for Er ³⁺ ion-doped silica-based optical fiber is characterized in that it has a resonator structure.

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